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POCreate Generic method constraining T to an Enum
 

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    <p>I'm building a function to extend the <code>Enum.Parse</code> concept that</p> <ul> <li>Allows a default value to be parsed in case that an Enum value is not found</li> <li>Is case insensitive</li> </ul> <p>So I wrote the following:</p> <pre><code>public static T GetEnumFromString&lt;T&gt;(string value, T defaultValue) where T : Enum { if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } </code></pre> <p>I am getting a Error Constraint cannot be special class <code>System.Enum</code>.</p> <p>Fair enough, but is there a workaround to allow a Generic Enum, or am I going to have to mimic the <code>Parse</code> function and pass a type as an attribute, which forces the ugly boxing requirement to your code.</p> <p><strong>EDIT</strong> All suggestions below have been greatly appreciated, thanks.</p> <p>Have settled on (I've left the loop to maintain case insensitivity - I am using this when parsing XML)</p> <pre><code>public static class EnumUtils { public static T ParseEnum&lt;T&gt;(string value, T defaultValue) where T : struct, IConvertible { if (!typeof(T).IsEnum) throw new ArgumentException("T must be an enumerated type"); if (string.IsNullOrEmpty(value)) return defaultValue; foreach (T item in Enum.GetValues(typeof(T))) { if (item.ToString().ToLower().Equals(value.Trim().ToLower())) return item; } return defaultValue; } } </code></pre> <p><strong>EDIT:</strong> (16th Feb 2015) Julien Lebosquain has recently posted <a href="https://stackoverflow.com/a/8086788">a compiler enforced type-safe generic solution in MSIL or F#</a> below, which is well worth a look, and an upvote. I will remove this edit if the solution bubbles further up the page.</p>
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    1. USVadim Ovchinnikov
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    1. COWhy are extension methods only for reference types?
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      1. USShimmy
    2. CO@Shimmy: As soon as you pass a value type to the extension method, you're working on a copy of it, so you can't change its state.
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      1. USGaro Yeriazarian
    3. COKnow it is an old thread, don't know if they changed things, but extension methods works fine for value types, sure they might not always make as much sense, but I have used "public static TimeSpan Seconds(this int x) { return TimeSpan.FromSeconds(x); }" to enable the syntax of "Wait.For(5.Seconds())..."
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